The experiments in Part I of this proposal will test the hypothesis that alterations in the structure and regulation of the GABA synthetic enzyme, glutamate decarboxylase (GAD), or of GABAA receptor polypeptides underlie the seizure disorders in animal models of epilepsy. Part I encompasses two specific aims: (1) to determine whether one of the genes encoding GAD or GABA receptor polypeptides is altered in one of the existing genetic mouse models of epilepsy, and (2) to determine whether the expression of GAD or GABA receptor genes is altered in several genetic and experimental models or epilepsy. The experiments proposed in Part II of this proposal will attempt to program the altered expression of GAD and GABA receptor polypeptides in cell lines and in transgenic mice. Part II encompasses three specific aims: (3) to program high level expression of GAD in subclones of existing cell lines, (4) to determine the mechanism of GABA release in these engineered cell lines, and (5) to determine whether seizure susceptibility is altered in transgenic mice with altered expression of GAD or GABA receptors. Direct injection of GABA agonists into the brain in some cases prevents seizure propagation and cell death. A long term goal of the experiments proposed in specific aims #3 and 4 is the production of engineered cell lines that could provide a continuing and regulatable source of GABA. Such "designer neurons" may be ultimately useful in transplantation therapies for intractable seizures or for such neurodegenerative diseases as Huntington's disease. If we succeed in producing cells that release GABA, either constitutively or in response to depolarization, we will then, in collaboration with other investigators, address the problems of transplantation into experimental animals and testing for seizure suppression.